158 TRANSLOCATION IN PLANTS 



a uniform development of a tension throughout the full 

 length of the sieve-tube system, any reduction in turgor 

 of the supplying leaf cells would correspondingly decrease 

 the rate of flow from these cells. Furthermore, with the 

 osmotic gradient leading in the wrong direction, as dis- 

 cussed under 3 a, the proposed transmission of tension is 

 of no avail. 



c. The partial emptying of leaves just prior to leaf fall 

 which has been observed by Swart (1914), Deleano and 

 Andreesco (1932), and others would seem to be another 

 instance of movement from a tissue of low osmotic concen- 

 tration or low turgor to one of higher concentration or 

 higher turgor. Deleano and Andreesco, however, found a 

 marked increase in hexoses during this period and sug- 

 gested that this increase maintained the turgor of the 

 cells and favored transport from them. I know of no 

 specific data, however, which actually give the relative 

 osmotic concentrations or turgors of these tissues. Several 

 investigators have observed that the lower leaves of a 

 shoot are likely to have lower osmotic concentrations 

 than the upper leaves. They also wilt more quickly when 

 water becomes deficient. According to the scheme of 

 Munch, these leaves should therefore be receiving foods 

 from the more turgid leaves. Phloem contents should 

 also move more readily to these leaves than to roots or 

 cambium at greater distances. I know of no data on 

 transport into or from the lower leaves, but from their 

 continued low content it seems unlikely that they act as 

 receiving organs. I have noticed the progressively increas- 

 ing flaccidity of the older leaves of Crassula portulaca 

 when these are supposedly giving up their contents to 

 the young shoots developing in their axils. Schumacher 

 (1931) observed an actual transport of 60 to 70 per cent 

 of the nitrogen from wilting flowers in a period of 24 hr. 



d. Still another problem related to translocation, which 

 would be diflficult of explanation according to the hypoth- 

 esis proposed by Munch, is that bearing on the matter 

 of dominance of one part over another, and of the seeming 



